Chapter 14

Focused cardiac ultrasound

Gabriele Via¹, Anthony Dean^2,3, Gabriele Casso¹, Brian Bridal Løgstrup⁴ and Guido Tavazzi⁵

¹Cardiac Anesthesia and Intensive Care, Cardiocentro Ticino, Lugano, Switzerland. ²Division of Emergency Ultrasonography, Dept of Emergency Medicine, University of Pennsylvania Medical Center, Philadelphia, PA, USA. ³Universidad de San Carlos de Guatemala, Guatemala City, Guatemala. ⁴Dept of Cardiology, Aarhus University Hospital, Aarhus, Denmark. ⁵University of Pavia, Anesthesia, Intensive Care and Pain Therapy, Anesthesia and Intensive Care, Emergency Dept, Fondazione IRCCS Policlinico San Matteo, Pavia, Italy.

Correspondence: Gabriele Via, Cardiac Anesthesia and Intensive Care, Cardiocentro Ticino, Via Tesserete 48, 6900 Lugano, Switzerland. E-mail: gabriele.via@winfocus.org

The use of FoCUS is becoming widely accepted as a tool to aid clinical decision making, especially in critical care, emergency medicine, anaesthesia and acute cardiac care. In these settings where cardiovascular/respiratory compromise may be challenging and rapidly evolving, FoCUS has the potential to provide crucial pathophysiological information. In this chapter, the concept, aims, technique and clinical applications of FoCUS are described, with an emphasis on its technique, how it relates to formal comprehensive echocardiography and its limitations.

Definition, aims and limitations

FoCUS represents a targeted application of echocardiography that is rapidly expanding in use in emergency and critical care medicine. It is a clinician-performed cardiac US test frequently based on standardised scanning protocols. It is performed by appropriately trained clinicians to obtain information needed in the management of unstable patients for time-sensitive clinical decision making [1, 2]. The primary goals of FoCUS are an understanding of the cardiovascular physiology/pathophysiology of the patient and the mitigation of diagnostic uncertainty. Furthermore, when FoCUS findings are sufficiently conclusive, they may allow a definitive diagnosis. If they do not, they may narrow the differential diagnosis, thereby accelerating the diagnostic/therapeutic process with potential savings in time, clinical resources and costs.

Although most commonly conducted at the bedside by noncardiologists using highly mobile or even portable US machines, FoCUS can be performed by any appropriately trained clinician regardless of his or her specialty, with any US machine capable of obtaining the necessary information [1, 2]. It can be performed within the hospital, as well as in any out-of-hospital setting in which unstable or emergently ill patients are being cared for. Such settings include hospital wards, emergency departments, operative theatres, intensive care units, pre-hospital and inter-hospital transport, and remote and austere environments.

FoCUS is targeted based on the clinical evaluation; it is informed by the clinical evaluation, and seeks to complement and augment it. Examples of typical questions to be addressed by FoCUS include: Why is this patient hypotensive/dyspnoeic? Might this patient benefit from volume resuscitation? Is major right ventricle (RV) systolic dysfunction responsible for the shock state of this patient? Another important distinction between FoCUS and the traditional echocardiographic examination is that many critical care and emergency sonologists are trained in LUS, allowing them to integrate this skill with their cardiac US evaluation. Currently, LUS is not a component of most echocardiology protocols, and the majority of echocardiologists are not trained or experienced in its use. Indeed, FoCUS represents the cardiac US application within a broader critical US praxis, which includes (as indicated by the patient’s clinical condition) evaluation of the lungs, pleural spaces, abdominal cavity and vascular system, and is frequently augmented by the use of US to guide invasive procedures [3]. Outside the emergency/critical care context, evidence also suggests an emerging role for FoCUS in the screening of cardiac disease in specific high-risk populations [1, 4].

Table 1 provides a detailed summary of how FoCUS differs from traditional comprehensive echocardiography.

There is clear evidence that noncardiology clinicians can be proficient in the skills required for FoCUS [1, 9–14]. The learning curve for FoCUS is shorter (and steeper) than that of comprehensive echocardiography, so that training programmes can be relatively short compared with those required for expertise in comprehensive echocardiography [1, 15]. However, given the heterogeneity of FoCUS literature in the training protocols, there are no data that precisely define and quantify the training and experience needed for competence in FoCUS, and the recommendations vary. The core components of a FoCUS training programme should be a theoretical part, hands-on training and image-interpretation training. According to several scientific bodies, there is general agreement that a brief introductory course, followed by the execution of at least 50–60 examinations performed under appropriate proctorship represents an adequate training for competency in the most basic FoCUS examination (evaluation for pericardial effusion, tamponade, acute intravascular volume depletion, acute RV failure, left ventricle (LV) systolic dysfunction and gross valvular abnormalities) [1, 2, 16–19].

It is important that clinicians are mindful that the test characteristics of FoCUS are different from those of comprehensive echocardiography, in the same way that portable and nonportable chest radiographs, chest CT and pulmonary CT angiograms all have different test characteristics. In particular, the training and experience of a clinical sonologist are often limited in comparison with those of imaging specialists, and the limitations of FoCUS in the context of the management of critically ill patients mean that it yields more limited information. For these reasons, the FoCUS practitioner in the critical care setting should have a low threshold for obtaining a comprehensive echocardiogram (as well as other diagnostic tests) in cases where findings are ambiguous or unclear, or where the clinical context suggests that the patient’s condition may be due to cardiac pathology that is not obtainable from the FoCUS examination (e.g. chronic heart disease, valvular disease). Recognition of specific limitations (e.g. frequently mechanical ventilation, or the immediate post-cardiac surgery setting) and of technical limitations of the US equipment is a component of FoCUS expertise. A clear definition of the FoCUS goals, purview and limitations is an important part of any FoCUS training curriculum. Conversely, traditional imaging specialists should be aware that the intensivist’s familiarity with the patient’s clinical condition, the integration of US evaluation of the lungs and other organ systems with the FoCUS examination, and the ability to perform the examination in real-time, concurrent with changes in the patient’s condition, may confer advantages on FoCUS over a comprehensive echocardiographic evaluation.

A final limitation that should be noted is that FoCUS is widely used in clinical settings outside those of traditional echocardiography (e.g. trauma, resuscitation and intensive care in general), and is frequently integrated into the US examination of other body areas. Discussion of the extensive uses of FoCUS in these settings is beyond the scope of this chapter.

FoCUS technique and equipment

A FoCUS examination does not require the execution of all the views of a comprehensive echocardiographic examination. A limited number of views (figure 1 and table 2) usually suffices to allow confirmation of findings [1]. Those most commonly used in the FoCUS examination are the subcostal long-axis (SLAX, also named subcostal four-chamber (S4CH)), subcostal inferior vena cava (SIVC), parasternal long-axis (PLAX), parasternal midpapillary short-axis (PSAX) and apical four-chamber (A4CH). The SLAX view is particularly useful in patients with chronic lung disease, or in mechanically ventilated patients. Whenever possible, a combination of views should be obtained, although this may not be possible in the critical setting. Ideally, each target structure as well as abnormal findings should be visualised in at least two different planes or views, provided the patient’s clinical status allows it.

Figure 1. Suggested standard set of views for FoCUS, with corresponding anatomical sections and planes. If compatible with the clinical scenario, a systematic approach going through all of these views is recommended. The upper left panel depicts where the probe is located on the patient’s chest in order to obtain the FoCUS views. For each of the five FoCUS views, the remaining panels provide a schematic description of: probe orientation (indicated on the torso image in each part), US cross-section through the heart (upper right on each part), anatomical plane (left on each part) and corresponding cardiac US view obtained (lower right on each part). The five views are: 1) subcostal long axis (SLAX, also named subcostal four-chamber (S4CH)), 2) subcostal inferior vena cava (SIVC), 3) apical four-chamber (A4CH), 4) parasternal long axis (PLAX) and 5) parasternal short axis (PSAX) (in this image, the midpapillary level is shown, but the left ventricle (LV) from apex to base can be scanned). For a better understanding of the US images of the heart obtained with each view, the arrow on the torso pictures indicates the orientation of the marker on the probe (yellow dot in the picture), while the yellow line on the margin of the US sector cutting the heart and of the anatomical plane picture indicates the side corresponding to the probe’s indicator, e.g. for A4CH, the probe indicator (yellow dot) is oriented on the left side of the patient, and the left-sided structures of the heart (LV and left atrium (LA)) are represented in the anatomical plane and in the US image on the side of the sector highlighted by the yellow line. RV: right ventricle; RA: right atrium; IVC: inferior vena cava; AscAo: ascending aorta; IVS: interventricular septum.

Recommendations regarding the most useful cardiac views in FoCUS are contradictory. In the critically ill nonventilated patient, the PLAX view seems to be the most easily obtained [20]. However, the SLAX and A4CH views offer several advantages: 1) they allow simultaneous visualisation of all cardiac chambers, providing the information required to screen for chronic cardiac disease (the advised preliminary target of each FoCUS examination; see later section), 2) especially in cardiac arrest scenario, the SLAX view is the most easily accessible one, and in the challenging mechanically ventilated patients it can be the only viable one, and 3) the SLAX view, with minimal probe manipulation, also quickly provides sonographic access to the inferior vena cava (IVC) (i.e. through the SIVC view). In extreme situations with the greatest time sensitivity, the two combined subcostal views may provide sufficient initial minimal information (although the FoCUS examination should be completed as soon as the clinical picture permits).

A systematic approach, going through multiple views in a protocolised fashion, is recommended to increase the accuracy of FoCUS [1]. The assumption is that going through most or all views of a FoCUS examination in a standardised way increases its screening capabilities for the various abnormalities and decreases the likelihood of missing findings or parts of the examination in clinically chaotic and stressful environments, such as in cardiopulmonary resuscitation. An example of FoCUS protocol for cardiac arrest, Focused Echocardiography Evaluation in Life support (FEEL), is described in figure 2 [5]. The echocardiographic modalities applied in FoCUS are represented by two-dimensional (2D) mode and motion mode (M-mode), as current evidence does not support the use of Doppler-based techniques in this setting [1]. When available and if compatible with time restraints of the clinical scenario, ECG-gated acquisition during a FoCUS examination may be helpful for better timing of cardiac events.

Figure 2. The Focused Echocardiography Evaluation in Life support (FEEL) protocol. This is a widely used protocol-based FoCUS approach that is designed to be integrated within the Advanced Cardiac Life Support (ACLS) protocols in cardiac arrest. FoCUS is performed if nonshockable rhythms are detected, and in an ACLS-conforming manner: only after five cardiopulmonary resuscitation (CPR) cycles, during the 10-s interval of the pulse check, and without interfering with resuscitation manoeuvres. VF: ventricular fibrillation; VT: ventricular tachycardia; PEA: pulseless electrical activity; EMD: electromechanical dissociation; ETCO₂: end-tidal CO₂.

FoCUS can be performed with any US machine capable of 2D cardiac imaging, from a full functionality platform to pocket-sized and hand-carried devices. The latter use a simpler technology and thus present relevant technical and diagnostic limitations in comparison with high-end US machines. When cardiac US was performed comparing experienced operators with high-end machines and with portable devices, results varied according to the targets of the examination considered, ranging from a good agreement [21, 22] to significant superiority of stationary high-end machines [23]. Several factors may potentially affect the quality and interpretation of the FoCUS information obtained with such highly portable devices, especially in situations in which suboptimal patient echogenicity poses a challenge: smaller and lower resolution of the screen, an intrinsic lack of complex image enhancement and artefact reduction capabilities, and the possibility of limited acquisition modifications [24]. Awareness of portable US machine limitations by FoCUS practitioners is extremely important: the ability to undertake a careful assessment of image quality and reliability should be part of any FoCUS competency-based training [1, 24].

FoCUS findings and patterns

FoCUS includes the assessment of a narrow list of evidence-based detectable targets [1, 19] (table 3). While there are numerous modalities used in comprehensive echocardiographic examinations to measure cardiac function and anatomy, many of these are time consuming and require training beyond that of the usual critical care or emergency sonologist. However, there are a few metrics that are relatively easy to assess, and with a trained eye these can often be rapidly evaluated by visual estimation with a degree of accuracy that is sufficient for critical clinical decision making [1, 9].

With appropriate training, visual pattern recognition of these findings (either in isolation or combination) can be learned relatively rapidly [1, 9–11]. Development of adequate visual pattern recognition skills usually requires review of large numbers of normal and pathological video clips, which is an important component of a training programme. The goal is to identify distinctive sonographic features that are associated with common and significant cardiocirculatory disease. This process is facilitated by the fact that, in many cases, “the sicker the patient, the grosser the FoCUS findings”. A description of these patterns is provided in table 4. Figure 3 provides examples of common FoCUS patterns in shock, some of which are also found as reversible causes of PEA.

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